# Example 9 -- nonlinearly shaded image colorscale
#
# Contributed 31 July 1996 by Dan Kelley <Dan.Kelley@Dal.CA>

# Create a HSB palette file, using 'perl' system command.
# You could do this with 'gawk' or other system commands,
# or you could create the file in matlab or a text editor,
# outside Gri.

# Note: tan is RGB=(210,180,140) in /usr/lib/X11/rgb.txt, in the X11
# 0 to 256 RGB coordinate system.  This is (0.820,0.703,0.547) in 
# the Gri's 0 to 1 rgb coordinate system.  This translates to
# (0.095,0.333,0.820) in the Gri hsb coordinate system.  (Note:
# a program to translate RGB to HSB is available from Dan 
# Kelley at Dan.Kelley@Dal.CA.)

\min = "-0.20"			# min image value
\a   = "-0.002"			# black if value is < \a
\b   = " 0.002"			# tan if between this and \a
\max = " 0.030"			# spectrum from \b up to this

set y axis 200    0 -25 -5
set x axis   0 2340 180 60
set image range \min \max

# NOTE: I have inserted comments into the example9.colorscale file,
# particularly to track the value of '$value', etc.  This is highly
# recommended procedure.

system perl <<"EOF"
open(CS, ">example9.colorscale") || die "Cannot open 'example9.colorscale'\n";
$value = \min;
$increment = (\max - \min) / 255;
for($i=0; $i<256; $i++) {
    if ($value < \a) {
        print CS "0.000 0.000 0.000 # value=$value is <\a so use black\n";
    } elsif ($value < \b) {
        print CS "0.095 0.333 0.820 # value=$value is between \a and \b so use tan\n";
    } else {
        print CS ($value - \b) / (\max - \b), " 1.000 1.000 # value=$value is > \b so use spectrum up to \max\n";
    }
    $value += $increment;
}
EOF

open example9.colorscale
read image colorscale hsb
draw image palette left -0.01 right 0.04 increment 0.01